Fluid pressure device



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United States Patent Ofice 2,747,370 Patented May 29, 1956 FLUID PRESSURE DEVICE William A. Traut, McAllen, Tex.

Application January 15, 1952, Serial No. 266,570

Claims. (Cl. 60-52) This invention relates as indicated to a fluid pressure device and more particularly to an accumulator of the fluid cushion type adapted to be inserted in a hydraulic pressure system.

Hydraulic pressure systems are commonly employed to operate piston cylinder assemblies of jacks, lift trucks, airplane landing gear, etc. Since it is desirable that relatively small pumps and motors be employed in most of these applications, it is ditficult to obtain rapid actuation of the piston cylinder assembly and it is therefore the usual practice to include an accumulator in the line to provide a reservoir of hydraulic fluid under pressure. One common form of accumulator comprises a globe having a rubber diaphragm across its diameter with a gas trapped in one-half of the globe behind the diaphram and with the other half of the globe or sphere in communication with the fluid pressure line. As liquid is admitted to the globe, it stretches the diaphragm and compresses the gas trapped therebehiud. Mechanical accumulators are also known utilizing a spring-backed plunger which is shifted against the force of such spring by liquid pumped into the cylinder within which such plunger is mounted.

Inasmuch as there is a tendency toward the employment of higher and higher pressures, various problems have been encountered in the construction and use of such prior art accumulators. Those employing gases such as nitrogen as a cushion medium are subject to leakage and also may be very dangerous due to the possibility of explosion when the gas therein has been highly compressed. In this connection it is understood that Government specifications for accumulators employed in military aircraft require that the maximum pressure in the gas chamber thereof shall not exceed 3000 p. s. i. This places a definite limitation on fluid cushion accumulators especially when it is considered that the mean operating pressure thereof will be somewhat lower than the maximum.

One object of this invention is to provide an accumulator for hydraulic pressure systems wherein the upper and lower limits of pressure in the fluid cushion chamber may be held reasonably close so as to afford a relatively high mean working pressure without exceeding the maximum pressure to which such accumulator is limited in the interests of safety. More specifically such object is to provide increased mean working pressure of the accumulator without increasing the upper limit of pressure in the cushion chamber thereof.

A further object of the invention is to provide an accumulator which will cost approximately one-half the cost of present accumulators and which will be small, compact, readily adjustable and substantially fool-proof.

As a more direct approach to the safety problem encountered in the employment of high pressures-in the accumulator chamber, it is a further object to employ, as the compressible medium in the chamber of the accumulator, a liquid. While liquids ,are of course considered as being practically non-compressible, at least when compared with gases, it is well known that when suflicient pressure is employed, a liquid may be compressed to a degree. Furthermore, should a break in the accumulator develop, while the liquid will of course be squirted out quite forcibly, there will be no such explosive action as is developed by highly compressed gases.

Other objects and advantages of this invention will appear as the description proceeds.

To the accomplishment of the foregoing and related ends, said invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various Ways in which the principle of the invention may be employed.

In said annexed drawings:

Fig. 1 is a diagrammatic illustration of a typical hydraulic pressure system including an accumulator in such circuit, such accumulator being shown in central longitudinal section;

Figs. 2 and 3 illustrate in central longitudinal section, modifications of the accumulator shown in Fig. 1;

Fig, 4 is a side elevational view showing the bed of a forging press, for example, supported by a plurality of fluid pressure devices of my invention; and

Fig. 5 is a central longitudinal sectional view of one of the fluid pressure devices employed to support the structure shown in Fig. 4.

Referring now to the drawings and more particularly to Fig. 1 thereof, a typical hydraulic pressure system is there shown including a ram 1 or similar fluid pressure actuated mechanism driven by a pump and electric motor assembly indicated diagrammatically at 2. Hydraulic pressure lines 3 and 4 interconnect such ram and pump and motor assembly through control valve 5 which may desirably be of the closed center type. Included in the hydraulic pressure system by means of line 6 is an accumulator indicated generally at 7. When in neutral position, control valve 5 will be operative to connect pressure lines 3 and 6 to build up a reservoir of hydraulic fluid under pressure from the pump in accumulator 7. In the operating position of valve 5, pressure line 4 is also connected into the above circuit to operate ram 1, the reservoir of hydraulic fluid under pressure in accumulator 7 preventing any material drop in pressure in the system, thereby affording rapid actuation of the ram. Following the operating cycle, the control valve will be shifted to relief position to interconnect line 4 and return line 8 to reservoir 9, permitting return of the ram. Since control valves operative as above described are conventional and well known, it is felt that a detailed description of the same is unnecessary.

It will of course be obvious that a control valve may be employed wherein the neutral and relief cycles occur simultaneously, that is, following the operating cycle of the ram. The latter will be permitted to return and discharge to the reservoir through the control valve while maintaining the accumulator in circuit with the pump and motor assembly 2. In this way, the accumulator will be constantly in standby condition.

Line 10 completes the hydraulic pressure circuit from the reservoir to the pump and motor assembly 2.

As is common in hydraulic pressure systems of this type, there may also be provided control means for the pump motor in the form of a piston-cylinder assembly 11 which is actuated by the discharge of the pump through pressure line 12 communicating with line 3. Thus, when the pressure in the hydraulic system reaches a predetermined maximum, it operates to shift the plunger of piston-cylinder assembly 11 in a direction to open switch 13 of the electric circuit 14 which drives the electric motor and pump assembly 2 to inactivate the latter. When the pressure again drops below a given point, the plunger of piston-cylinder assembly 11 will return under the=influence-of compression spring 15, again-cutting in the-electric circuit -14 to thepump and motor assembly 2.

Referring further to Fig. 1, the accumulator 7 there shown will beseen to comprise a cylinder 16 having a cylinder head I? screwed on to one end'of the same. Such cylinder head is formed with a-ithreaded orifice 17' to,:provide a connection with-line 6 of the hydraulicipressure system. Cylinder 16 has secured to its other end end by means of arc welding, for example, a metal block .18. A piston :19-isadapted to bereciprocated in cylinder- 16 under influence of fluidpressure from line 6 and is provided with a piston rod 20 extending through an opening provided in block 18. The variable space defined'by the piston 19, cylinder head 17 and cylinder 16 constitutes a reservoir for fluid of the hydraulic pressure system to be drawn upon to;provide quick actuation of ram 1 when the latter is to be operated. Welded to the right-hand end of block 18 is a heavy walled shell 21 forming a chamber 22 therein adapted to be filled with a-fluid cushion-medium, and int-owhich rod 25). is adapted to extend upon movement to the right of piston 19. An appropriate seal is provided around rod 20 within block 18 by packing 23 -(shown a chevron packing) compresssed against a shoulder in such block 18 by gland nut .24 threaded in such block.

A bleeder hole 25 is provided in block 18 to permit the escape from and entry of air into cylinder 16 on the rod side of piston :19 as the latter is reciprocated. A port 26 is provided in the wall of shell'2l for filling the chambertherein with-liquid, such port being closed with a suitable plug. Plug 27 threaded into an opening in shell 21 is provided to aflord a pre-charge portfor introduction of additional fluid under pressure whereby the fluid within the chamber may be compressed to an initial pressure-of 1-090 or 2000 p. s. i., for example. Such plug has an axial passage 28 therethroug'h normally closed bya check valve 29 to prevent the out-flow of fluid.

When the ,pump and motor assembly 2 is operated to develop pressure in the hydraulic pressure system which connects to port 17', such pressure will act on the piston 19 to shift the same to the right, filling cylinder 16 with a reservoir o-fhydraulic fluid, 'and'forcing piston rod 20 into chamber 22. As will be seen, the rod 20 is of relatively small cross-section as compared with the dimensions of .chamber 22 so that despite a relatively large movement of the rod into such chamber, the total volume of the latter will be reduced only to a small degree. Put another way, chamber 22 may be said to'be laterally enlarged with respect to the transverse dimensions of the rod. Accordingly, while such accumulator provides a substantial reservoir of hydraulic fluid pressure in the hydraulic system'by movement of piston 19 to the right, the change in pressure within chamber 22 will be relatively small when a gas is used as the cushion medium. In this way, it is-possible to maintain the limits of pressure of the cushion medium in chamber 22 Within fairly close limits in contrast .to the ordinary arrangement wherein the total space for the cushion medium is reduced proportionately (and thu the pressurethereof increased proportionately) to piston movement. Since the limits of pressure of the cushion medium are thusmaintained within fairly close limits,itis possible to increase substantially the mean-working pressure without exceeding the maximum pressure imposed by certain specifications.

Chamber 22 may be filled with a liquid such as oil rather than a gaseous cushion medium. Liquids are of course compressible to a degree under suflicient pressure. Thus, in the form illustrated in Fig. 1, since the area of the piston 19 exposed to the pressure of the hydraulic fluid system via line 6 is much greater than that of the end of rod 20, a much greater unit pressure will be exerted at the end of thelatter than against thepiston, so

that sufliciently high pressures in chamber 22 may be obtained actually to compress the liquid therein. Again, it may be noted that the piston rod even when fully inserted into chamber 22 takes up but a small portion of the total volume of the latter (because such chamber is laterally enlarged with respect to the rod) so that a relatively long reciprocationof piston 19 may be permitted without exceeding the limit of compressibility of the liquid in the chamber. Thus, the fluid pressurereservoir of the hydraulic system may be comparatively large and capable of maintaining a fluid pressure reserve even though rather heavily drawn upon by suchappliances as ram 1, for example, but the accumulator device itself may be considerably smaller than has been common in the past.

As in the case of a gaseous cushion medium, the accumulator chamber 22 may be pro-charged with liquid. While of course only a small additional amount of liquid may thusbe forced into the chamber, an'initial pressure of for example 2000 "p. s. i. may thus be developed-in the chamber.

In Fig. 2 is shown a slightly modified form of accumulator but which likewise is adapted to employ either a liquid or a gaseous cushion medium. The same comprisesa cylinder 30 having a metal block 31 welded or otherwise securedto one vendthereof and a second metal block 32 threadedly engaged in the other end. Port 33 inthe-latter block provides for communication with line 6 ofthe hydraulic system for example. A piston 34 is reciprocable within cylinder 30 and with the latter defines the hydraulic fluid reservoir .35 which may be drawn upon to actuate fluid pressure-mechanisms. The cushion chamber 36 is formed-within such piston, with bleeder port 37 providing an opening for initially filling such chamber, then closedby plug 33. Movable into and out of such chamber .36 as the pistonis reciprocated within cylinder 30 is an axial rod39 secured in block 31. An appropriate seal between the rod 39 and piston 34 is provided by chevron packing 4'0 and gland nut-41 threaded into the piston. A bleeder hole 42 is'provided in the wall of the cylinder to permit entry and escape of air as the piston reciprocates. A pre-charge passage 43 extends axially through the rod 39 so that additional-fluid maybe pumped into chamber 36, check valve 44 preventing outflow of fluid therethrough.

As in the illustration first described, the displacement of rod 39 as compared with the total volume of chamber 36 is relatively small even when it has fully entered the latter, since-such chamber is laterally enlarged with respect to thetransverse dimensions of the rod. The upper and lower'limits of pressure within the chamber may therefore be held fairly close. Likewise here the accumulator chamber may be charged with a liquid and because ofthe difference in area between the piston head -45 exposed to'the pressure of the hydraulic fluid pressure system and the end of rod 39, a comparatively high pressure may be built up against the latter, sufficient to compress such liquid. As pointed out above, since the displacement of rod 39 even when fully inserted in chamber 36 is-very small, a sizable reservoir of hydraulic fluid may be pumped into reservoir 35 without exceeding the limits of compressibility of the liquid in such chamber as the rod moves thereinto.

*Still another form of my invention is illustrated in Fig. .3. The accumulator therein illustrated comprises a cylinder 46 having a metal'block '47 Wfildfld or otherwise secured to "one end and an annular nut 48 threadedly engaged inthe other end. Piston 49 is reciprocable within such cylinder and together with the latter defines a reservoir-50 :adapted to be filled with fluid from the hydraulic pressure system'through communication port 51 in cylinder head 47. Piston 49 includes a hollow axially extendingplunger portioni52 reciprocable in-head 48 -(:an appropriate seal being provided as shown). A plurality-. ofports '53 provide communication between the annular space 54 (defined by such plunger, piston and cylinder wall) and chamber 55 within the plunger. Thus, a cushion medium may fill not only chamber 55 but also annular space 54 and ports 53 as well. A pre-charge port 56, provided in the outer end of such plunger, permits the cushion medium to be pumped into the chamber under pressure, check valve 57 preventing the outflow of fluid.

In this form, when the accumulator is connected at 51 in a hydraulic pressure system, such as for example that shown in Fig. 1, the pressure developed in such system will act on the piston 49 to move the latter to the right thereby reducing annular space 54 and compressing the cushion medium with which the chamber 55 is charged. However, the cushion medium is compressed only a relatively small amount due to the fact that it is only the annular space 54 which is diminished while the chamber 55, which Jgreatly exceeds the maximum volume of annular space 54, remains unchanged in volume. Thus, it is possible to maintain the pressure of the cushion medium within fairly close limits. Here again a liquid may be used as the compressible cushion medium. Since the area of the piston head greatly exceeds that of the annular surface 58 acting to compress the cushion medium, the necessary pressure for compressing a liquid cushion medium may be obtained.

Figure 4 illustrates a structure which includes as part of the combination still another form of fluid pressure device employed as a shock dampener. The terrific impact of a forging press, for example, results in heavy shock vibrations to its support and surrounding installations. In order to lessen such shock, I provide one or more of my novel fluid pressure devices to support the bed 59 of the machine or other structure. Such fluid devices are indicated generally at 60 and illustrated more in detail in Fig. 5 This form of the device is rather similar to that illustrated in Fig. 3, the same including a cylinder 61 resting upon a support 62 and having a piston 63 movable therein. Such piston has an extension or plunger 64 formed to define with the inner wall of the cylinder an annular space 65, such plunger extending into an opening in support 62 when the piston moves downwardly under impact from the forging press or like structure supported by legs 66 resting thereon. A cushion medium, either gaseous or liquid may fill such annular space 65 and chamber 66A, the latter being formed within the plunger and communicating with space 65 through port 67. Chevron packing 68 and annular gland nut 69 threaded in the lower end of the cylinder provide an eflective seal against the escape of the cushion medium. A bleeder-port 70 formed in the cylinder head allows the accumulator to be filled with the cushion medium (a suitable plug, not shown, being provided to close such port), and a pre-charge port 71 in the lower end of the plunger permitting additional cushion medium to be pumped in under pressure, check valve 72 preventing the outflow of fluid. An annulannut 73 threaded in the upper end of cylinder 61 prevents piston 63 from rising out of the cylinder. In this embodiment, as in the others previously described, it is contemplated that a liquid or gaseous cushion medium may be employed.

In each form of accumulator disclosed, the relatively movable piston and cylinder members are so formed as to define a cushion chamber which is enlarged or reduced only a relatively small amount as compared with the degree of relative movement of the members necessary to elfect such change. Thus, the limits of pressure of the cushion medium may be held close and at the same time a rather large reservoir of hydraulic fluid may fill the accumulator to be drawn upon by the various fluid pressure mechanisms operated by the hydraulic system. It should be noted that by maintaining the upper and lower limits of pressure in the cushion chamber close together, the mean Working pressure may be raised for a given maximum pressure. This means that smaller pistoncylinder assemblies for operating jacks, airplane landing gear, etc., may be employed since the higher mean working pressure will aflord the same amount of work although operating on a piston of smaller area. Furthermore, since smaller piston-cylinder assemblies, for example, are suitable to do the same amount of work (because of higher working pressures), less displacement of the accumulator piston is required. This, of course, permits the size of the accumulator itself to be reduced.

I have also found that an accumulator employing a liquid cushion such as oil is much safer than those charged with a high pressure gaseous medium. Accumulators employing gases may of course be very dangerous due to the possibility of explosion when the gas therein has been highly compressed. While a liquid may be squirted out quite forcibly, should a leak develop, there will not be the explosive action developed by highly compressed gases.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

I therefore particularly point out and distinctly claim as my invention:

1. A fluid pressure device comprising a cylinder, a piston reciprocable therein, a fluid inlet port at one end of said cylinder, an axial extension of said piston of slightly less diameter than the interior of said cylinder, an annular cylinder head fitting said extension for reciprocation of the latter therethrough and closing the end of said cylinder opposite the fluid inlet end thereof, thereby forming a small annular chamber defined by said cylinder, said piston, said extension and said head, a chamber within said extension of much larger capacity than the maximum capacity of said annular chamber, a passage connecting said respective chambers through the wall of said extension adjacent said piston, and a fluid entry port for said chamber in the outer end of said extension.

2. A fluid pressure device comprising a cylinder, a piston reciprocable therein, a fluid inlet port at one end of said cylinder, an axial extension of said piston of slightly less diameter than the interior of said cylinder, an annular cylinder head fitting said extension for reciprocation of the latter therethrough and closing the end of said cylinder opposite the fluid inlet end thereof, there by forming a small annular chamber defined by said cylinder, said piston, said extension and said head, a chamber within said extension of much larger capacity than the maximum capacity of said annular chamber, a passage connecting said respective chambers through the wall of said extension.

3. A device in accordance with claim 2 in which said chambers are filled with a slightly compressible liquid.

4. A fluid pressure device comprising a cylinder, a piston reciprocable therein, an axial extension of said piston of slightly less diameter than the interior of said cylinder, an annular cylinder head fitting said extension for reciprocation of the latter and closing an end of said cylinder, thereby forming a small annular chamber defined by said cylinder, said piston, said extension and said head, a chamber within said extension of much larger capacity than the maximum capacity of said annular chamber, and a passage connecting said respective chambers through the wall of said extension.

5. A device in accordance with claim 4 in which said chambers are filled with a slightly compressible liquid.

References Cited in the file of this patent UNITED STATES PATENTS 1,334,281 Constantinesco Mar. 23, 1920 1,450,372 Irish Apr. 3, 1923 2,276,016 Brantly Mar. 10, 1942 (Other references on following page) 7 UNITED STATES PATENTS Tyler May 19, 1942 Christensen Aug. 20, 1946 Ashton Apr. 20, 1948 Gruss June 22, 1948 Bachrnan July 25, 1950 'Bingham May 29, 1951 8 Gruss Jan. 8, 1952 Helm Jan. 22, 1952 Conway Nov. 18, 1952 FOREIGN PATENTS Great Britain Mar. 21, 1917 France Mar. 22, 1921 

